1. Field of the Invention
The present invention relates to cylinder locks and, particularly, to cylinder locks which incorporate side bars to enhance mechanical strength and thereby improve the ability to resist defeat through the application of torque to the cylinder. Specifically, this invention relates to enhancing the security afforded by side bar type cylinder locks by increasing the number of possible key combinations of such locks while simultaneously reducing the possibility of manufacture of key blanks which may be cut to form unauthorized keys for such locks. Accordingly, the general objects of the present invention are to provide novel and improved articles and methods of such character.
2. Description of the Prior Art
Cylinder locks which employ side bars are well-known in the art. Early examples of such locks may be seen from U.S. Pat. Nos. 2,003,086 and 2,426,104. A more recent example of a side bar lock, wherein generally L-shaped tumblers which cooperate with the side bar are reciprocated through coaction thereof with a slot in the side of the blade of a cooperating key, may be seen from U.S. Pat. No. 4,756,177. While side bar locks have many applications, a typical use environment is to control access to a cache of coins such as, for example, in a parking meter. The use of a side bar lock in such an application is dictated by the enhanced ability of these locks to resist defeat by the application of torque to the lock cylinder.
A consistency in the field of security devices is the desire, both by lock manufacturers and users, for improvements which will reduce the possibility of unauthorized access through defeat of a lock. Such improvements may take the form of increased mechanical strength and/or increased xe2x80x9cpick resistancexe2x80x9d. The latter type of improvement may, for example, be accomplished by increasing the number of possible combinations.
The selection of a complex keyway profile and/or variation of the number and orientation of the pin tumbler arrays will not eliminate the possibility of defeat of a cylinder lock. This fact, in part, results from the ready availability of key blanks having blades which, either as manufactured or as shaped using conventional key-cutting machines, can be xe2x80x9ccutxe2x80x9d to produce an unauthorized key which will operate a lock. Thus, the most common manner of defeating a cylinder lock consists of the formation of an unauthorized key from a commercially obtained key blank having a blade profile which matches the lock keyway cross-section. While security against defeat by unsophisticated villains may be achieved by incorporating sufficient mechanical strength in a lock, the ultimate degree of security can be accomplished only through the exercise of key control.
Cylinder locks which generally satisfy the above-discussed key control criteria, and particularly cylinder locks systems which include a unique key as a component thereof, are disclosed in U.S. Pat. Nos. 5,819,567 and 5,823,030.
The present invention provides a novel and improved cylinder lock and lock system and, in so doing, adapts the operational concept of above-referenced U.S. Pat. Nos. 5,819,567 and 5,823,030 to a side bar lock. A side bar lock in accordance with the present invention is characterized by enhanced resistance to defeat by both xe2x80x9cpickingxe2x80x9d and overpowering.
A lock in accordance with the invention, for each side bar, is provided with at least a first locking segment which is carried by, and movable relative to, the core. Each such locking segment includes a projection, which normally extends into the keyway, and a portion which cooperates with the associated side bar. In the absence of a proper key in the keyway, the side bar is prevented from moving out of engagement with an elongated receiver, i.e., a cam groove, in the lock shell by interference between the side bar and a surface on the locking segment. An authorized, i.e., proper, key will include a camming projection which, through cooperation with the projection on the locking segment, causes the locking segment to move relative to the core and side bar. In a preferred embodiment, proper amount and direction of such movement will place the side bar in registration with the deeper portion of a stepped notch in the locking segment whereby, if all other code parts of the lock combination are satisfied by the xe2x80x9cbittingxe2x80x9d on the key, the application of torque to the key will result in the side bar being cammed out of the cooperating receiver in the shell.
The above-mentioned other code parts of the lock combination are defined by an array of reciprocal tumblers. These tumblers, in a preferred embodiment, include extensions which project into the keyway for engagement by longitudinal groove(s) in the side(s) of the key blade, the groove(s) typically having straight code parts and angled transition parts. In a preferred embodiment the tumblers, on the sides opposite to the extensions, are provided with slots. These tumbler slots define part of the lock code and cooperate with fingers extending from the side bar. The tumblers may, in the interest of enhancing pick resistance, be provided with multiple slots of different depth, only one of which is sufficiently deep to satisfy the code.